The continuing evolution of microprocessors has made them economically feasible for a variety of applications varying greatly in complexity. Embedded microprocessors and microcontrollers have become ubiquitous due to their flexibility in design and computational power in control. As microprocessors continue to evolve, clock speeds, throughput, and associated power dissipation continue to increase.
Advances in technology have enabled more and more devices to be placed on a single substrate. However, as packing factors increase, each design must provide for heat dissipation due to the considerable heat generated by active devices. In this regard, low voltage microprocessors have been developed to reduce heat generation. For many applications, passive heat dissipation is not sufficient, even though low voltage devices are utilized.
In addition to the heat generated by the microprocessor and other active components, many applications subject the microprocessor and its associated components to a wide range of ambient operating temperatures. For example, microprocessors used in vehicular applications are often mounted in regions of the vehicle which experience a wide range of operating temperatures. Microprocessors may be mounted on the engine, in the transmission, in the passenger cabin, and the like. These microprocessors require a robust design to assure reliability and durability throughout the life of the vehicle while continually being subjected to temperature swings which may range from below -50.degree. C. to above 100.degree. C., for example. As such, the ambient temperature of the microprocessor may adversely affect its operation if not properly designed.
In general, as temperature increases, the channel resistance of a typical MOSFET device will also increase, which may lead to thermal runaway. Operation of these devices at excessive junction temperatures will ultimately lead to an intermittent or permanent failure.